In a drug delivery device, a piston within a cartridge that contains drug may be displaced with respect to the cartridge in the distal direction by a piston rod which moves in the distal direction with respect to the cartridge. Thereby, a dose of drug can be expelled from the cartridge. In order to provide for a reusable device, after the cartridge containing the drug has been emptied, the piston rod often has to be moved back from a distal end position to a proximal starting position.
WO 2009/049885 A1 describes an injection device which can be reset by removing the cartridge and thus disengaging the toothings of a steering element and a cylindrical sleeve, so that the piston rod can freely rotate.
WO 01/72361 A1 describes a one-way clutch means for use in an incrementing mechanism suitable for use in a medical injector device.
WO 02/092153 A2 describes a medication injector apparatus with a resettable cartridge plunger drive assembly including an axially floating nut, a cartridge plunger engaging screw, and a drive clutch movable with the nut.
WO 03/008023 A1 describes a medication dispensing apparatus having a manually operable plunger axially shiftable relative to the apparatus housing. A priming mechanism is operated by rotating an externally accessible driver portion.